Many work sites, such as engineering work sites and materials handling sites that involve the operation and movement of vehicles, equipment and machinery (for example, trucks, cranes, tractors, forklifts, conveyors, diggers, crushers, underground mining equipment and the like) often require special measures to minimise risk of injury and other damage, and to meet particular safety requirements.
The prior art includes warning systems such as proximity detection and collision avoidance systems that have been developed to assist workers or equipment operators to detect the proximity of another worker or machinery so as to avoid collision.
Some proximity detection systems use radio communication in which an electromagnetic field generated by a transmitter can be detected by receivers (carried by personnel) when the receivers are within a predetermined range of the transmitter. This allows measures to be taken to avoid collision or accident.
However, the strength and therefore the range of the electromagnetic field generated by a transmitter can be affected by factors of its operating environment. For example, the signals from one transmitter can sometimes interfere with the signals from one or more other transmitters. Moreover, metal objects in an operating environment can have the effect of significantly altering the circuit inductance and hence the resonant frequency of the transmitter, thereby affecting the strength of the electromagnetic field generated by the transmitter.
In addition, changes in material properties of the circuitry components, such as changes in properties of dielectric, insulation, conductor and inductor core materials can occur, for example, as the circuitry components deteriorate with age and use, and/or become affected by temperature, pressure, humidity and other environmental variables.
These factors have had the effect of limiting the effectiveness of existing proximity detection systems in some work places. The electromagnetic field generated by these proximity detection systems can be weak, unreliable, and/or prone to interruption or interference.
In transmitters used in existing proximity detection systems, it is known to use a variable inductor or a variable capacitor to compensate for any changes in the performance of the transmitter during set up and operation in a particular environment. These variable inductors and capacitors are typically adjusted by manual control or using a servomechanism. These solutions either involve field intervention, or introduce additional complexity and consequent expense and risk.
The present invention aims to address at least in part one or more of the disadvantages or problems described above, or at least to provide the industry with a useful choice.
In this specification, where a document, act or item of knowledge is referred to or discussed, such a reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date part of common general knowledge, or known to be relevant to an attempt to solve any problem with which this specification is concerned.